1. Field of the Invention
The present invention relates to a surface processing apparatus that irradiates electron beams onto an object to be processed such as a semiconductor wafer or a glass substrate under a vacuum atmosphere, thus modifying a resist or an insulating film.
2. Description of the Related Art
Conventionally, in the field of semiconductor device manufacturing, lithography processing is carried out in which a circuit pattern is transferred onto a semiconductor wafer W using a resist, and then curing processing is carried out in which the resist is cured, thus increasing the mechanical strength of the resist. The curing of the resist in the curing processing is carried out by modifying the resist through electron beam (EB) irradiation.
FIG. 4 is a view useful in explaining a conventional electron beam irradiation apparatus (surface processing apparatus) used in curing processing.
In FIG. 4, the electron beam irradiation apparatus 50 is comprised of a processing chamber 51 inside which a semiconductor wafer W is subjected to curing processing, a mounting stage 52 that is provided in the processing chamber 51 and on which the semiconductor wafer W is mounted, a plurality of electron beam (EB) tubes 53 that are provided in an upper wall of the processing chamber 51 such as to face the mounting stage 52, an exhaust system 54 that controls the pressure inside the processing chamber 51, and a gas introduction port 55 from which a suppressing gas such as nitrogen or a processing gas such as argon for generating ultraviolet radiation is introduced into the processing chamber 51. The semiconductor wafer W is mounted on the mounting stage 52 provided inside the processing chamber 51, and thus faces the EB tubes 53.
Each of the EB tubes 53 is comprised of a cylindrical vacuum vessel, and a cover provided at one end of the vacuum vessel; inside the vacuum vessel are a filament and a grid to both of which a high voltage is applied. Thermal electrons are discharged from the filament that has been heated by the high voltage, the discharged thermal electrons are accelerated by an accelerating voltage generated by the grid to form an electron beam, and the electron beam passes through the cover and is irradiated out of the EB tube 53.
According to the electron beam irradiation apparatus 50, a resist on the semiconductor wafer W is cured through the electron beams from the EB tubes 53 being irradiated onto the resist (see, for example, Japanese Laid-open Patent Publication (Kokai) No. 2002-182000).
In general, resists cured through such curing processing are made of any of various materials and have any of various layer thicknesses, and hence depending on the magnitude of the accelerating voltage, the electron beam energy may be too great for the material and thickness of the resist layer, and hence the electron beams may pass through the resist layer and penetrate into an underlayer below the resist layer in the semiconductor wafer W, whereby the underlayer may be subjected to undesired processing; as a result, the properties of an insulating film, devices or the like provided on the underlayer may change.
Currently, research is thus being carried out into various electron deceleration control methods for subjecting the electrons in an electron beam to deceleration control and thus reducing the electron beam energy.
Of such electron deceleration control methods, a well known method is one in which an intermediate electrode is provided between the EB tubes and the mounting stage, and a predetermined DC voltage is applied to the intermediate electrode, whereby an electric field is generated in a direction such as to decelerate the electrons in the vicinity of the intermediate electrode, and hence the electrons are decelerated.
However, with the method described above in which an intermediate electrode to which a predetermined DC voltage is applied is provided between the EB tubes and the mounting stage, a power source for applying the DC voltage and wiring inside the processing chamber for connecting the power source and the intermediate electrode together are required, and in particular measures must be taken to insulate the wiring inside the processing chamber to prevent abnormal electrical discharge; there is thus a problem that the construction of the surface processing apparatus becomes complex.